1. Field of the Invention
The present application relates generally to thermoelectric devices, and more specifically to thermoelectric devices with interface materials.
2. Description of the Related Art
Thermoelectric (TE) devices are solid state heat engines and can operate in two modes as heat pumps as well as thermoelectric power generators (TEG). In general, heat pumps are used to move heat from a high temperature to a low temperature reservoir (cooling devices) or to move heat from a low temperature to a high temperature reservoir (heating devices). Heat pumps can use electrical power input to operate. Thermoelectric power generators typically operate in a reverse thermodynamic cycle and can use heat input to generate electricity. In these devices, heat can be moved through the thermoelectric device from a high temperature to a low temperature reservoir and a portion of this heat can be converted into electricity. Examples of high and low temperature reservoirs include, but are not limited to, gas or liquid heated/cooled heat exchangers, bodies undergoing exothermic or endothermic reactions, surfaces of vessels in which endothermic or exothermic reactions are occurring, and radiating surfaces.
In typical TE devices, a solid-state engine comprises p- and n-type thermoelectric materials (for example Bi2Te3, Sb2Te3, PbTe, SnTe, CoSb3, FeSb3 semiconductors, and their alloys and metals) that are electrically connected either in series or parallel connections. Materials commonly used for electrical connections are copper (Cu), nickel (Ni), iron (Fe), and other metals with high electrical and thermal conductivities. These electrical connections are referred to as hot and cold shunts. Hot shunts are electrical connections on the hot side of the thermoelectric device and cold shunts are electrical connections on the cold side of the thermoelectric device. Hot and cold shunts are commonly in thermal communication (e.g., in direct contact) with the high temperature and low temperature reservoirs respectively. In some instances, hot and cold shunts are radiatively coupled to the heat source and the heat sink, respectively.
During manufacture and normal operation of TE devices, shunts are periodically heated and cooled and undergo thermal expansion. The TE materials bonded to the shunts can expand differently with temperature. In general, elongation (∈=ΔL/L) of TE materials and shunts is driven by each material's coefficient of thermal expansion (CTE) and local material temperature (Tm), ∈=CTE·Tm. Differences in CTE and Tm between a shunt and TE material can result in increased stress at the interface between them. These stresses are usually the main failure mechanism and the main reason why TE materials are not sintered integrated with shunts.